Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus including the zoom lens. The zoom lens may be applicable to, for example, an imaging apparatus with an image pickup element, such as a digital still camera, a video camera, a monitoring camera, and a broadcasting camera, and an imaging apparatus such as a camera using a silver-halide photographic film.
Description of the Related Art
Imaging apparatuses, such as a digital still camera or a video camera, employing a solid-state image pickup element continue to be improved to have sophisticated applications and the entire body has been downsized. A zoom lens used in such apparatuses is desired to have a short total lens length and a high zoom ratio. Further, to maintain the aim of providing affordable imaging apparatuses with reduced body size, it is required to reduce the weight and the cost of the lens.
A known zoom lens having a short total lens length and a high zoom ratio includes a positive-lead type zoom lens, which is, a zoom lens including, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having negative refractive power. Further, to reduce the weight and the cost of the lens, some known zoom lenses include a lens made of a material other than glass, for example, a resin lens made of a resin material.
As a positive-lead type zoom lens including a resin material, in zoom lenses discussed in Japanese Patent Application Laid-Open Nos. 2012-220872 and 2012-226224, a resin lens having positive refractive power is used in a first lens unit and, further, a resin lens having negative refractive power is used in a third lens unit.
Compared with a glass lens, a resin lens generally has a greater variation of refractive index due to a temperature change or a manufacturing error and has more influence of a change in shape due to expansion and shrinkage of the resin material. This tends to easily cause deterioration of optical performance in resin lenses because the amount of focus error and spherical aberration deviation due to temperature change or a manufacturing error becomes greater than in glass counterparts. In a positive-lead type zoom lens composed of a relatively small number of lenses, since refractive power of each lens becomes strong, deterioration of optical performance due to temperature change is likely to be caused in the entire zoom area. Therefore, improvements in resin-based zoom lenses remain highly desirable.